I got my most recent lab results, and it turns out that my urine sodium is low, but my urine protein is mostly fine (just a bit low, nothing to worry about). This is what my nephrologist had to say in email:
Low sodium in urine means dehydrated. Low urine specific gravity means dilute urine, meaning ratio of water to solute intake is high.
And these are the questions I emailed back to her, after doing some online research:
1. I assume I have "hyponatremia," and that it is "hypervolemic hyponatremia" (since that seems to be the kind that most often occurs with kidney disease). I've been trying to drink more water since I saw you in December, since we thought I might be dehydrated, but apparently dehydration can also be caused by drinking too much water compared to sodium intake? So should I be drinking less water or continuing to increase my sodium intake? Or do you recommend some other course of action entirely? I'd been trying to do both, but maybe I shouldn't?
2. The definitions of hyponatremia I've seen online describe it as a blood sodium level of below 130, but mine was measured (just a couple weeks ago) as 142. My urine sodium level, though, is lower than normal, <275. What does this combination (normal blood sodium but low urine sodium) mean?
3. Why would my urine sodium (and, I guess, subsequent creatinine and GRF levels) have changed since August? My diet hasn't changed, and I've actually been drinking *less* water since I went off lithium in early July 2013. My thirst has gradually declined in the months since the labs on August 8th, so why would hyponatremia develop?
4. Could diabetes inspidus be involved somehow? Back when I was taking lithium, it definitely seemed like I had it, but I don't know if it has gone away. I know my urine is still diluted.
5. Do I need more tests?
6. I think I should see a dietician once we understand what's going on. Can you refer me?
In the meantime, I'm trying to drink normally (except perhaps a bit more Gatorade to replace some of the water) and get a bit more sodium until I hear back from her. She's sick right now and doesn't know if she'll be back in the office on Monday, so it might be a few days before I get any answers.